Many existing reverse shoulder systems (RSA) require a baseplate and a glenosphere. These systems generally differ from one another in how the baseplate is fastened to the glenoid cavity and how the glenosphere becomes engaged to the baseplate. In some systems, the baseplate may be fastened to the glenoid cavity of the scapula by a plurality of screws and a glenosphere having a convex joint surface may be screwed into the baseplate using an axial threaded feature and/or taper locked to a periphery of the baseplate. In other systems, the glenosphere may engage the baseplate solely via a taper connection. Generally, a compression fit is not preferable between the glenosphere and baseplate due to the potential need for separating the two components once engaged to one another.
In cases where the glenosphere becomes engaged to the baseplate through either a threaded or taper connection, the glenosphere and baseplate may become separated after a certain length of time. This may cause the glenosphere to tilt with respect to the baseplate or in some cases even completely separate therefrom. In either situation, the baseplate and glenosphere become misaligned.
Some systems include first fastening a central screw to a glenosphere and then guiding the connection between the baseplate and glenosphere via the central screw. Guiding the connection between the baseplate and glenosphere is generally an important consideration due to minimal access and visibility that the surgeon may have during a RSA procedure. Access to the baseplate is generally narrow making it relatively difficult for the surgeon to have the visibility needed to correctly align the engagement between a baseplate and glenosphere.